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Physiology 1 > Properties of Special Circulation > Flashcards

Properties of Special Circulation Flashcards

1
Q

What are the 3 main characteristics of special circulations?

A
  1. Special requirements met by the circulation
  2. Special structural or functional features of the circulation
  3. Specific problems relating to that circulation
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2
Q

Describe the coronary circulation

Where do they begin?

What do they do, and what are the coronary arteries?

What do the cardiac veins carry and where do they carry it to?

What is the coronary sinus?

A
  • Two coronary arteries originate from the left side of the heart at the beginning (root) of the aorta, just after it exits the left ventricle. These arteries supply blood to the heart itself. It includes the right and left coronary arteries which divide.
  • Cardiac veins carry blood with a poor level of oxygen, from the myocardium to the right atrium. Most of the blood of the coronary veins returns through the coronary sinus. Coronary sinus enters the superior vena cava.
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3
Q

What are the 2 special requirements of the myocardium muscle?

A
  • Needs a high basal supply of O2 – 20x resting skeletal muscle
  • Increase O2 supply in proportion to increased demand/cardiac work
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4
Q

What are the 3 special structural features of the heart?

A
  • High capillary density
  • Large surface area for O2 transfer
  • Together these reduce diffusion distance to myocytes….diffusion time is proportional to distance squared – so O2 transport is fast.
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5
Q

In terms of capillaries and fibres, what are the special structural features of the heart?

A

Cardiac muscle contains high numbers of fibres and capillaries giving rise to shorter diffusion distances.

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6
Q

What are the 4 special functional features during normal activity?

A
  • High blood flow - 10x the flow per weight of rest of body.
  • Relatively sparse sympathetic innervation
  • High nitric oxide released leading to vasodilatation – less sympathetic tone, quite dilated which allows for high O2 extraction.
  • High O2 extraction (75%) – average in body is 25%
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7
Q

What are the 3 special functional features during increased demand?

A
  • Coronary blood flow increases in proportion to demands.
  • Production of vasodilators (adenosine, K+, acidosis) out-compete relatively low sympathetic vasoconstriction.
  • Circulating adrenaline dilates coronary vessels due to abundance of 2-adrenoceptors
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8
Q

Oxygen unloading to myocardium – during normal activity

Bohr shift

A
  • Coronary sinus blood returning to right atrium from myocardial tissue has a greater carbon dioxide content due to high capillary density, surface area and small diffusion difference.
  • The high CO2 and low pH has shifted the curve to the right meaning that haemoglobin has less affinity for oxygen and more O2 is given up to the myocardial tissues.
  • The myocardium is able to extract 75% of the oxygen as opposed to typically 25% in other tissues
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9
Q

How does Increased O2 requirement produce increased blood flow?

A

Extraction is near max during normal activity.

Therefore to provide more O2 during demand, we must increase blood flow.

Myocardium metabolism generates metabolites to produce vasodilatation, increase blood flow
(metabolic hyperaemia).

eg. Adenosine, produced by ATP metabolism and is released from cardiac myocytes. Also, increases in pCO2, H+, K+ levels.

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10
Q

Human coronary arteries are functional end-arteries

Ischaemic Heart Disease

A

Coronary arteries are functional end-arteries and therefore decreased perfusion produces major problems. Therefore, a whole area of the heart is starved of oxygen. The tissue can die, and wont conduct, having serious consequences.
Heart is very susceptible to sudden and slow obstruction

Sudden - acute thrombosis, produce myocardial infarction

Slow - atheroma (sub-endothelium lipid plaques) chronic narrowing of lumen, produces angina.

Systole obstructs coronary blood flow.

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11
Q

What happens if you get an occlusion in your left coronary artery?

A

Occlusion leading to obstruction of blood flow to anterior (front) left ventricle – myocardial infarction

  • ischemic tissue, acidosis, pain (stimulation of C-fibres)
  • impaired contractility
  • sympathetic activation
  • arrhythmias
  • cell death (necrosis)
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12
Q

Describe the resistance in a normal artery/ arteriole at rest

Describe the resistance in a normal artery/ arteriole during exercise

A

At rest, resistance is low in a large coronary artery. Then resistance is high in the arterioles

During exercise, we still have a low resistance to flow in artery. We get metabolic vasodilation of arterioles to reduce resistance, so we have an increased blood flow to meet oxygen demands

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13
Q

Describe the resistance in a stenosis artery/ arteriole at rest

Describe the resistance in a stenosis artery/ arteriole during exercise

A

In artery, stenosis increases resistance. Metabolic hyperaemia occurs at rest, so blood flow meets needs. Resistance is high in arteries. Resistance in arterioles is reduced.

During exercise, arterioles further dilate to reduce resistance, but total resistance is still high due to stenosis. Oxygen demand cannot be met, angina develops. Resistance is high in the artery and in arterioles resistance isn’t reduced enough

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14
Q

When can blood flow through the coronary arteries

A

Blood can only flow through the coronary arteries during diastole

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15
Q

What 3 factors lead to reduced coronary flow?

A
  1. Shortening diastole, eg. high heart rate.
  2. Increased ventricular end-diastolic pressure, eg. Heart failure (aortic stenosis, stiffening of ventricle).
  3. Reduced diastolic arterial pressure, eg. hypotension, aortic regurgitation. This means the heart cannot relax enough
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16
Q

Describe how temperature regulation is involved with circulation

A
  • Blood flow delivers heat from the body core
  • Radiation (proportional to skin temperature)
  • Conduction to skin – convection from skin (skin temp)
  • Sweating (latent heat of evaporation)
  • Skin is an organ and temperature can range from 0oC to 40oC (briefly) without damage (poikilothermic rather than homeothermic).
17
Q

Describe how the circulation is involved with defence

A

Defence against the environment

• Lewis triple response to trauma (increased blood flow)

18
Q

Describe Arterio-venous anastomoses (AVAs)

A
  • Direct connections of arterioles and venules expose blood to regions of high surface area.
  • Convection, conduction, radiation, evaporation.
  • These open and close to bypass blood flow to different areas.
19
Q

What do Sympathetic vasoconstrictor fibres do?

A

• Release noradrenaline acting on α1 receptors

20
Q

What do Sudomotor vasodilator fibres do?

A
  • Acetylcholine acting on the endothelium to produce nitric oxide.
  • Driven by temperature regulation nerves in hypothalamus.
21
Q

How does the body help heat loss?

A

Increase ambient temperature and cause vaso and venodilation

22
Q

How does the body help to conserve heat?

A

Decrease ambient temperature causes vaso and venoconstriction

severe cold can cause paradoxical cold vasodilation

Cold temperature receptors in the hypothalamus control sympathetic activity to skin and hence skin blood flow

23
Q

Effect of ambient temperature on skin blood flow - what happens when you get into cold water

A
  1. When you first enter cold water, you get cold-induced vasoconstriction
  2. After a while of being cold sympathetic nervous system is turned off and you get vasodilation
24
Q

What causes cold-induced vasoconstriction?

A

Sympathetic nervous systems react to local cold by releasing noradrenaline which binds to alpha 2 receptors on the vascular smooth muscle in skin

Alpha 2 receptors bind NA at lower temperatures that alpha 1

This conserves heat

25
Q

What causes paradoxical cold vasodilation?

A

Caused by paralysis of sympathetic transmission.
Long term exposure leads to oscillations of contract and relax.

This protects against skin damage

26
Q

What is Cutaneous perfusion & core temperature?

A

what happens when you get hot

27
Q

What are the causes of Cutaneous perfusion & core temperature?

A

Sweating
• Increased sympathetic activity to sweat glands
• mediated by acetylcholine.

Vasodilatation
• Increase sympathetic sudomotor activity such that acetylcholine act on endothelium to produce NO which dilates arterioles in extremities.

28
Q

Describe the effect of Baroreflex/RAAS/ADH-stimulated vasoconstriction of skin blood vessels

A
  • Blood directed to more important organs/tissues during loss of BP following haemorrhage, sepsis, acute cardiac failure.
  • Mediated by sympathetic vasoconstrictor fibres + adrenaline + vasopressin + angiotensin II. Responsible for pale cold skin of patient in shock.
  • During haemorrhage warming up body too quickly may reduce cutaneous vasoconstriction and be potentially dangerous – blood flow to skin not vital organs/tissues.
29
Q

Describe emotional communication and response to skin injury

A

Emotional communication
• eg. blushing (sympathetic sudomotor nerves)
Response to skin injury
• The Lewis triple response

30
Q

Describe the pathway of the Lewis triple response to trauma

A
  1. Trauma
  2. C fibre
  3. Main axon
  4. Dorsal root ganglion
  5. Axon collateral
  6. Substance P causing vasodilation and mast cell degranulation, releasing histamine
31
Q

What are the 3 effects from the Lewis triple response

A

Local redness: the site of trauma
Local swelling: Inflammatory oedema (wheal)
Spreading flare: Vasodilation spreading out from the site of trauma

32
Q

What does the C-fibre axon reflex do it terms of its function?

A

Mediates the flare to trauma

33
Q

What happens in terms of the immune system?

A

Increased delivery of cells and immune system cells to the site of trauma to fight pathogens

34
Q

What does prolonged obstruction to flow cause?

A
  • Severe tissue necrosis…

* bed sores - heels, buttocks, weight bearing areas

35
Q

How can prolonged obstruction to flow be avoided?

A
  • Shifting position / turning causing reactive hyperaemia (on removal of compression)
  • High skin tolerance to ischemia
36
Q

What happens when you stand for to long and what is it called?

A

Postural hypotension / oedema due to gravity
• Often standing for long periods in hot weather will decrease central venous pressure (hypotension) and increased capillary permeability (oedema).
• Feel faint, rings of fingers can be tighter.

Physiology 1 (72 decks)

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